Lithium Intercalation Compounds spectrum and as C12 (1.2 mmol) by color and molecular weight. Unreacted CF3SFC1 was also recovered. Reaction of CF3SF4CI with NOCI. A 50-ml Pyrex glass vessel which contained equimolar amounts (1.5 mmol) of CF3SF4CI and NOCl was heated at 150' for 12 hr. After separation, CF3N0, SiF4, and unreacted CF3SF4Cl were identified by using infrared. Chlorine was also found. The yield of CF3NO was 40%. Similar products were found after uv irradiation of the reaction mixture in a quartz vessel. Preparation of CF3SF4SF4CF3. A 2:l mmol mixture of CF3SF4Cl and hydrogen in a 300-ml Pyrex vessel was photolyzed by using a Hanovia Utility model uv lamp for 10 hr. After trap-to-trap fractionation, a 50% yield of CF3SF4SF4CF3 was found in a trap cooled to -78'. Preparation of CF3SF4NC(Cl)CF3. Irradiation of a mixture of C F C N (6 mmol) and CF3SF4Cl (5 mmol) in a quartz vessel for 12 hr gave, after trap-to-trap separation and subsequent purification by using a 6-ft FS-1265 GC column, CF3SF4NC(Cl)CF3 (2.5 mmol) and CF3SF4SF4CF3 (1 mmol). Preparation of CF3SF4NCC12. Using the same reaction and purification conditions as above, CF3SF4Cl ( 5 mmol) was reacted with ClCN to give CFsSF4NCC12 (2.3 mmol) and CF3SF4SF4CF3 (1 mmol). Preparation of CFBF4NCFCF3. One millimole of CF3SF4NC(Cl)CF3 was condensed onto an excess of CsF in a 75-ml Hoke reaction vessel and was heated at 100' for 4 hr. Nearly quantitative conversion to CF3SF4NCFCF3 occurs. Preparation of CF3SF3=NCF3. When CF3SF4NCC12 was condensed on excess CsF in a Hoke vessel and allowed to remain at 25' for 10 hr, a volatile compound identified as CFBF3NCF3 in >99% yield was found. Preparation of CF3SF4N(CI)CF3. After 5 hr at 60°, a mixture of CF3SF3NCF3 (1 mmol) and C1F (1.5 mmol) reacted to form CFBF4N(Cl)CF3 in a yield >98%. For final purification an 8-ft Kel-F column was used. When CsF is present, CFBF4N(CI)CF3 is formed in similar yields at 25'. Preparation of CF3SF4N(H)CF3. Hydrogen fluoride (2 mmol) was reacted with CF3SF3NCF3 (1 mmol) in a 75-ml Hoke reaction vessel at 60' for 5 hr. The reaction mixture was transferred into a second Hoke vessel which contained NaF. After 12 hr at 25', the volatile mixture was separated by trap-to-trap distillation. Retained in a trap at -78' was CF3SF4N(H)CF3 in 40% yield. An equimolar mixture of CFBF4N(Cl)CF3 (1 mmol) and HCI was condensed into a Pyrex vessel at -183' and allowed to warm slowly to 25". A quantitative yield of CF3SF4N(H)CF3 was found.
Inorganic Chemistry, Vol. 15, No. 1, 1976 17 Preparation of CF3SF4N(CI)CF2CF3. Into a 75-ml vessel at -183' which contained CsF were condensed CFSF4N=CFCF3 (2 mmol) and C1F (3 mmol). The mixture was allowed to remain at 25' for 8 hr. A quantitative yield of CF3SF4N(Cl)CF2CF3 was obtained. Preparation of CFSF4N(H)CFKF3. In a Pyrex vessel at 25', equimolar amounts of CFBF4N(Cl)CF2CF3 (1 mmol) and HCl were reacted to give C F ~ S F ~ N ( H ) C F Z CinF>99% ~ yield. The spectral, analytical, and thermodynamic data for these new compounds are given in Tables I1 and Table 111.
Acknowledgment. Fluorine research at the University of Idaho is supported by the National Science Foundation and the Office of Naval Research. We thank Mr. Stan Morse for mass spectra and Mr. Chit Srivanavit for nuclear magnetic resonance spectra. Registry No. CF3SF4CI,25030-42-6; CF3SF4SF4CF3, 1580-11-6; CF3SFdNC(Cl)CF3, 56868-52-1; C F ~ S F ~ N C C ~56868-53-2; Z, CF3SF4NCFCF3, 56868-55-4; CF3SF3eNCF3, 56868-56-5; CF3SF4N(Cl)CF3, 56868-57-6; CF3SF4N(H)CF3, 56868-58-7; CF3SF4N(Cl)CF2CF3, 56868-59-8; CF3SF4N(H)CF2CF3, 56868-60-1; ClF, 7790-89-8; CF3SF3, 374-10-7; NOC1,2696-92-6; CRNO, 334-99-6; Hz, 1333-74-0;CFsCN, 353-85-5; ClCN, 506-77-4; CSF, 13400-13-0; HF, 7664-39-3; HC1, 7647-01-0; CF3SSCF3, 372-64-5.
References and Notes C. W. Tullock, D. D. Coffman, and E. L. Muetterties, J . Am. Chem. SOC.,86, 357 (1964).
J. I. Darragh and D. W. A. Sharp, Chem. Commun., 864 (1969). T. Abe and J. M. Shreeve, J . Fluorine Chem., 3, 187 (1973). J. I. Darragh, G. Haran, and D. W. A. Sharp, J . Chem. SOC.,Dalton Trans., 2289 (1973). H. L. Roberts, J . Chem. SOC.,3183 (1962). R. C. Dobbie, J . Chem. Soc., 1555 (1966). N. H. Ray, J. R. Case, and H. L. Roberts, J . Chem. SOC.,2066,2070 (1961). G. M. Burch, H. Goldwhite, and R. N. Haszeldine, J. Chem. SOC.,1083 (1963). F. W. Hoover and D. D. Coffman, J . Org. Chem., 29, 3567 (1964). H. W. Sidebottom, J. M. Tedder, and J. C. Walton, Trans. Faraday SOC.,65, 2103 (1969). R. E. Banks, R. N. Haszeldine, and W. D. Morton, J . Chem. SOC.C, 1947 (1969). R. A. De Marco and J. M. Shreeve, J . Fluorine Chem., 1, 269 (1971). M. Lustig and J. K. Ruff, Inorg. Chem., 4, 1444 (1965). G. H. Sprenger, K. J. Wright, and J. M. Shreeve, Inorg. Chem., 12,2890 (1973).
Contribution from Bell Laboratories, Murray Hill, New Jersey 07974
Convenient Preparation and Physical Properties of Lithium Intercalation Compounds of Group 4B and 5B Layered Transition Metal Dichalcogenides DONALD W. MURPHY,' FRANCIS J. DI SALVO, GEORGE W. HULL, Jr., and JOSEPH V. WASZCZAK
Received March 18, 1975 AIC50199I n-Butyllithium in hexane solution has been found to be a mild and efficient reagent for intercalation of lithium into the layered MX2 compounds (M = Ti, Zr, Hf, V, Nb, Ta; X = S, Se, Te), most of which were prepared in this study. All the compounds attained a limiting composition of LiMX2 except We2 which formed LizVSez. For the group 5B compounds this is more lithium than can be intercalated at high temperatures or from lithium-ammonia solutions. The tellurides, which decompose under previous reaction conditions, were intercalated using n-BuLi. Crystallographic, magnetic susceptibility, pressed pellet dc conductivity, and superconductivity data are reported. Only the LiZrX2 compounds were superconducting. All compounds have a low room-temperature resistivity (10-2-10-3 fl cm in pressed powders) except Li2VSez which has p 2 w = ~ 6 X 103 fl cm. LizVSez contains V*+ having S = 3/2 and g = 1.98 and possible antiferromagnetic ordering below 20'K. Only LiTiSez gave any indication in magnetic susceptibility of a possible charge density wave instability similar to those observed in dl MX2 compounds.
A number of alkali metal intercalates of the groups 4B,5B, and 6B layered transition metal dichalcogenides have been reported.1-7 These compounds have been prepared either by combination of the elements at high temperature, by treating
the parent MX2 with a solution of the alkali in liquid ammonia, or by treatment with lithium naphthalide. These methods have drawbacks, particularly for lithium intercalation. Hightemperature methods may lead to decomposition or only partial
18 Inorganic Chemistry, Vol. 15, No. 1, 1976
intercalation. The alkali metals also attack quartz reaction tubes a t high temperature. Reactions in liquid ammonia usually give products which have incorporated ammonia. Although the ammonia may usually be removed a t elevated temperatures in vacuo (25OoC for LiTiS27), the space taken up by the ammonia during reaction may in some cases prevent full intercalation of the alkali.8 Many transition metals can also catalyze formation of LiNHz from lithium in liquid ammonia. Some physical properties of 2H-TaS2 have been shown to be affected by sulfur removal in pure liquid ammonia.9 Such sulfur removal may occur with alkali metal ammonia solutions and with other MX2 as well. Electron transfer catalysts such as naphthalene in solvents such as THF or D M E have been used, but cointercalation of solvent and/or catalyst may occur. A procedure for preparation of these compounds under milder conditions alleviating the drawbacks of hightemperature methods and ammonia solutions would be of value in preparing pure compounds for measurement of physical properties. We report here that n-butyllithium (n-BuLi) in hexane solution is a mild reagent for the intercalation of lithium into group 4B and 5B metal dichalcogenides, free of complicating side reactions.10 In addition to many previously known intercalation complexes, this method has allowed us to prepare lithium intercalation compounds of the ditellurides, which decompose under reaction conditions used previously. Surprisingly, we have also prepared Li2VSe2, the first example of such stoichiometry in these compounds. Although a number of LixMX2 compounds have been prepared, few physical measurements (except x-ray data) have been reported, probably because of the moisture sensitivity of the compounds11 and their varying stoichiometries. W e have tried to fill this void with crystallographic, magnetic susceptibility, conductivity, and superconductivity data for the compounds prepared. Of particular interest is the possibility of charge density wave (cdw) instabilities in the group 4B LiMXz since they are isoelectronic with the group 5B MX2, many of which have cdw instabilities.12-14 At onset of the cdw in group 5B MX2 compounds, the magnetic susceptibility usually decreases providing a possible indicator of the cdw. Experimental Section All of the MX2 compounds used were prepared by published procedures.ls.16 n-Butyllithium (2.4 M in hexane) was purchased from Alfa Products and was standardized periodically by titration with n-butyl alcohol in xylene using 1,lo-phenanthroline as indicator according to the procedure of Watson and Eastham.17 All reactions were carried out under argon in dried Schlenkware. All transfers of the products, which are moisture sensitive, were made in an argon filled inert atmosphere box. In a typical reaction 3.00 ml of n-BuLi (7.06 mmol) was added to 0.5410 g of ZrSez (2.17 mmol) in a Schlenk tube. The mixture rapidly became hot enough to boil the hexane and the ZrSez (gold-brown powder) became dark green. After half an hour the mixture was heated to 60°C for 10 hr to ensure completion of the reaction. No exfoliation was observed in these reactions. The product was filtered in the Schlenk frit and washed with ether. The filtrate containing excess n-BuLi was titrated with 0.953 M n-butyl alcohol in xylene using 1,lO-phenanthrolineindicator. The titration required 5.15 ml of the alcohol-xylene solution, allowing calculation of the stoichiometry as LiowZrSe2. We feel the stoichiometry calculations are good to &2%. Early experiments with dilute n-BuLi (-0.5 M ) at room temperature gave only partial intercalation. In general an excess of n-BuLi was used, but with VSez this led to formation of a hexane soluble red side product (x-ray fluorescence measurements indicate it contained both V and Se). To inhibit this decomposition LiVSez and Li2VSez were prepared with stoichiometric amounts of n-BuLi. Addition of 1,lO-phenanthroline indicated all the n-BuLi had been consumed. Capillary tubes for Debye-Scherrer x-ray powder photographs were loaded in the glove box and sealed with wax and then with a flame outside the box. A Teflon holder with a tight-fitting top was used
Murphy, Di Salvo, Hull, Waszczak for superconducting TCmeasurements by the usual low-frequency ac susceptibility method.16 Samples for magnetic susceptibility (-200 mg) were loaded in thin-wall quartz tubing inside the glove box, evacuated, back filled with 20 Torr of helium, and sealed prior to measurement using the Faraday technique previously described.18 Four point conductivity measurements were made using powdered samples pressed into a Plexiglas die with brass plungers which served as the current leads. The voltage leads were 1/32 in. stainless steel screws sharpened to a point and screwed into the die to make contact. The hexagonal layered compounds have highly anisotropic conductivities,lg for example 2H-NbSez p parallel to the c axis/p perpendicular to the c axis is 30 at 30OoK.20 Several of the parent compounds were measured and gave p values within a factor of 5 of literature values for PI. Since these are pressed powders, with not all the particles aligned, these higher values were not unexpected. Results and Discussion The reaction to give LiMX2 from n-BuLi and MX2 is conceptually analogous to the use of electron-transfer reagents such as lithium naphthalide. Although n-BuLi is mainly a covalent hexamer in hexane, its chemistry is conveniently thought of as arising from Li+(n-Bu)-. The intercalation then is conceptually electron transfer from Bu-, the lithium ion intercalating to balance the charge. The advantage over electron-transfer reagents is that commercially available solutions in a noncoordinating solvent (hexane) may be used avoiding any solvent intercalation. Octane and LiMX2 are the sole products as shown in eq 1. The formation of octane MX,
+ n-BuLi [MX,- + Bus + Li+] +
LiMX, .+ 1 octane
was confirmed by gas chromatography (GLC). Besides titration of excess n-BuLi, measurement of octane formation by G L C is another method of determining stoichiometry. Stoichiometry was also determined for LiTaSz and LiNbSe;, by addition of excess standard acid solution to LiMX2 and titrating the acid consumed by the reaction in eq 2. This LiMX, + HY MX, + ‘/zH, + LiY (2) -+
method is unsatisfactory for the group 4 compounds because of varying degrees of hydrolysis of the chalcogenides to give amphoteric oxides. The limiting composition in all cases studied except VSez appears to be one lithium. No attempt was made to prepare less than fully intercalated compounds, except for LizVSez. High-temperature methods and preparations from ammonia solution generally give Li/M I 0.8 for the group 5 compounds.5B8 In cases where our measured stoichiometry was low (Lio.ssTiSe2 and 1T-LiomTaSz) no attempt was made to improve it. In the case of VSez the limiting composition is LizVSez, which is the first example of this stoichiometry for the dichalcogenides. The existence of LizVSez is apparently a result of the greater stability of V2+ compared to the divalent ions of the other group 4B and 5B metals. W e believe that LizVSez is a layered compound based on maintenance of hexagonal symmetry on going from VSez to LizVSez (see crystallographic results) and since the isoelectronic VC12 is also known to have the Cd12 structure.21 We were unable to prepare Li2VS2 from the known LiVS2. In retrospect it is somewhat surprising that the Ti compounds do not form Li2MX2 compounds since Tic12 also has the CdI2 structure22 and the empty t2g band could accommodate two electrons. The group 4B MX2 are very reactive toward n-BuLi, generally exothermic enough to boil the hexane solution, whereas the N b and Ta compounds were not, even though color change of MX2 from steel gray to silvery was rapid. Reaction of VSe2 with n-BuLi was quite exothermic after a short induction period. All the LiMXz were moisture sensitive,l* especially the group 4B LiMXz which were on occasion pyrophoric.
Inorganic Chemistry, Vol. 15, No. I, I976 19
Lithium Intercalation Compounds Table I. Hexagonal Unit Cell Dimensionsf i
Compds 1T-Li .,TiS, lT-Li,.,,TiSe,
~s-L~,.,z~s, lT-Li,.,,ZrSe, lT-Li,.,,ZrTe, lT-Li,.,,HfS, lT-Li,.,,HfTe, lT-Li,.,VSe, 1T-Li 2.0 VSe, 2H-Li1.,,NbSe, Li,.,, NbTe, e 2H-Li0.,,TaS, IT-Li,.,,TaS, 2H-Li0.,,TaSe, Li,.,,TaTeZe Pd V, Si
c,
a, A .
3.423 (3.405) 3.643 (3.535) 3.672 (3.662) 3.732 (3.770) 4.014 (3.950) 3.548 (3.635) 3.992 (3.949) 3.58 (3.35) 4.01 3.502 (3.45) 3.75 (3.75) 3.314 (3.315) 3.343 (3.346) 3.449 (3.434) 3.75 (3.74)
a
6.222 (5.690) 6.431 (6.004) 3 X 6.306 (5.813) 6.637 (6.138) 6.942 (6.630) 6.344 (5.837) 7.092 (6.651) 6.40 (6.10) 6.45 2 X 6.80 (2 X 6.27) 7.00 (6.68) 2 X 6.392 (2 X 6.05) 6.461 (5.860) 2 x 6.801 (2 x 6.348) 7.10 (6.72)
1 0 6 x (300°K): ~ emu/mol 177 246 16' 13' -14' -7
P , 0 cm (298°K) 1.4 x 10-3 (5 x 10-3)
6.8 X (1) 8.7 x 10-3 7.4 x 109.5 x 10-3 (>io51 4.2 x 1 0 - 2 (9 x 10-4) 6 x lo3 1-35 x 10-3(4 x 10-4) 2.72 x 1 0 - ~ 7.0 x 10-4
815 d
-44
Tc, "K
